(a) Field of the Invention
The present invention relates to a fuel cell system. In particular, the present invention relates to a fuel cell system that has a structure that improves the electrical connection between the stack and a load.
(b) Description of the Related Art
A fuel cell is a system that produces electrical energy using chemical reaction energy between hydrogen contained in hydrocarbons such as methanol, and air containing oxygen.
Fuel cells are classified into various categories including phosphate fuel cell, molten carbonate fuel cell, solid oxide fuel cell, and polymer electrolyte or alkali fuel cell. Although each of these different types of fuel cells operates using the same principles, they differ in the type of fuel, catalyst, and electrolyte used, as well as in operating temperature.
A polymer electrolyte membrane fuel cell (PEMFC) has been developed recently. The PEMFC has excellent output characteristics, a low operating temperature, and fast starting and response characteristics compared to other fuel cells. In the PEMFC, hydrogen that is generated by converting methanol or ethanol may be used as a power source in a wide range of applications such as vehicles, homes, buildings, and electronic devices.
The basic components of the PEMFC are a stack, reformer, fuel tank, and fuel pump. The stack forms the main body of the fuel cell. The fuel pump supplies fuel from the fuel tank to the reformer. The reformer converts the fuel to produce hydrogen gas and supplies the hydrogen gas to the stack. The hydrogen gas reacts with oxygen in the stack to thereby generate electrical energy.
In the PEMFC system, the stack is structured to include numerous unit cells that comprises a membrane electrode assembly (MEA) and separators that are provided on both sides of the MEA. An anode and a cathode are provided opposite each other with an electrolyte layer interposed therebetween to form the MEA.
Further, the separator may comprise a bipolar plate that separates each of the MEAs. The separator also provides a pathway through which hydrogen and oxygen, which are required for fuel cell reaction, are supplied to the anode and cathode of the MEA. In addition, the separator couples the anode and cathode of each MEA in series.
Hydrogen is supplied to the anode and oxygen is supplied to the cathode via the separator. The hydrogen is oxidized in the anode, and the oxygen is reduced in the cathode. Electricity is generated by the flow of electrons that occurs during these reactions. Heat and moisture are also generated.
Each unit cell provides a voltage of about 0.5 to 0.7 V, and as a plurality of unit cells are stacked and are serially connected, the stack produces a voltage that is proportional to the total unit voltages of all the unit cells. The electricity is then separated according to the predetermined voltage required by a load. For example, the required voltages for circuit elements, CPUs or driver ICs of electronic devices such as laptops or mobile communication terminal devices, are separated through a separately installed DC-DC converter which allows the prescribed voltage to then be applied to each load.
A conventional fuel cell system needs space for the DC-DC converter to fit in the fuel cell system, which increases the size of the system and complicates the structure of the system. In addition, since parasitic power is additionally required for driving the DC-DC converter, the efficiency of the system is decreased.